Natural Periodic Electrostatic Spraying of Liquids

Liquid issuing from the bore of a metallic capillary tube maintained at a high potential may, under certain conditions, be dispersed in the form of regular current pulses of charged droplets. This phenomenon is well known but not fully understood. The pulsation process is considered in some detail, and experimental data obtained during the electrostatic dispersion of pure and impure glycerol, in air and under vacuum, are presented. The variations of pulse characteristics with capillary voltage are studied together with cinephotography of the pulsating liquid meniscus at the tip of the capillary. Dripping and periodic spraying modes are identified. In air, corona discharges severely perturb and limit the spraying mode. In the case of impure glycerol (doped with an ionizable salt) spraying in vacuum, highly charged particles, probably cluster ions, are emitted at the beginning of each pulse.